Power-Stage Antenna Integrated System with High-Strength Shaft

ABSTRACT

Disclosed is a microwave antenna assembly that includes proximal and distal radiating sections and a junction member. The proximal radiating section includes inner and outer conductors and DC power and neutral conductors. The inner conductor is disposed within the outer conductor and the DC power and neutral conductors are disposed radially outward therefrom. The junction member mates the distal and proximal radiating sections such that the distal and proximal radiating sections are positioned relative to one another. The junction member further includes a microwave signal amplifier (MSA) that receives a signal at a first energy level from the inner and outer conductors and a DC power signal from the DC power and neutral conductors. The MSA amplifies the signal from the first energy level to an additional, greater energy level. The junction member provides the microwave signal at the additional energy level to the proximal and distal radiating sections.

BACKGROUND

1. Technical Field

The present disclosure relates generally to microwave systems anddevices. More particularly, the present disclosure relates systems anddevices for microwave and millimeter-wave signal transmission,amplification and energy delivery to tissue.

2. Background of Related Art

In the treatment of diseases such as cancer, certain types of cancercells have been found to denature at elevated temperatures (which areslightly lower than temperatures normally injurious to healthy cells).These types of treatments, known generally as hyperthermia therapy,typically utilize electromagnetic radiation to heat diseased cells totemperatures above 41° C. while maintaining adjacent healthy cells atlower temperatures to insure that irreversible cell destruction does notoccur. Other procedures utilizing electromagnetic radiation to heattissue also include ablation and coagulation of the tissue. Suchprocedures, e.g., such as those performed for menorrhagia, are typicallyperformed to ablate and coagulate the targeted tissue to denature orkill the tissue. Many procedures and types of devices utilizingelectromagnetic radiation therapy are known in the art and are typicallyused in the treatment of tissue and organs such as the prostate, heart,and liver.

Electronic heating of tissue may be accomplished by at least twomethods. A first method of electronic heating utilizes the production orinduction of an electric current in tissue. An electric current may beproduced between two electrodes, between an electrode and a return pador the current may be induced by an oscillating electric field. As such,heating with an electric current requires the tissue to be conductive orat least partially conductive.

A second method of electronic heating, which utilizes dipolar rotationwherein heat is generated by the movement of molecules by an electricfield, is known as dielectric heating. Dielectric heating requires theuse of energy in or around a microwave frequency and generates heat inboth conductive and nonconductive tissues.

The basic components of the microwave energy delivery system are similarto the components that comprise a conventional microwave ablation systemand included a power source and impendence matching circuit to generatemicrowave energy and an electrode means for delivering the microwaveenergy to tissue. The microwave generator circuit connects to theelectrode by any known suitable connection. Present microwave energydelivery systems include a microwave generator that connects to amicrowave energy delivery device, i.e., a tissue penetrating or catheterdevice, via a semi-rigid coaxial cable.

While many advances have been made in the field of electrosurgicalmicrowave ablation, a conventional electrosurgical microwave systemstill includes separate components for microwave signal generation,microwave signal transmission and microwave energy delivery (i.e., agenerator, coaxial cable and delivery device).

SUMMARY

The present disclosure moves away from the prior art systems thatprovides individual components performing separate and distinctivefunctions. The task of microwave signal amplification is distributedbetween the microwave generator and a power-stage device therebyeliminating the need for the energy transmission device to transmit ahigh power microwave energy signal.

The present disclosure relates to a microwave antenna assembly forapplying microwave energy. The assembly includes a proximal radiatingsection, a distal radiating section distal the proximal radiatingsection and a junction member. The proximal radiating includes an innerconductor, an outer conductor, a DC power conductor and a DC neutralconductor, each extending therethrough. The inner conductor is disposedwithin the outer conductor and the DC power conductor and DC neutralconductor are disposed radially outward from the outer conductor. Thejunction member mates the distal radiating section and proximalradiating section such that the proximal radiating section and thedistal radiating sections are fixedly positioned relative to one anotherby a mechanically-engaging joint. The junction member further includes amicrowave signal amplifier configured to receive a microwave signal at afirst energy level from the inner conductor and the outer conductor andconfigured to receive a DC power signal from the DC power conductor andthe DC neutral conductor. The microwave signal amplifier amplifies themicrowave signal from the first energy level to an additional level(e.g., a second energy level), the additional energy level being greaterthan the first energy level. The junction member is further configuredto provide the microwave signal at the additional energy level to theproximal radiating section and the distal radiating section.

The proximal radiating section and distal radiating section are adaptedto radiate upon transmission of radiation through the antenna assembly.The length of the proximal radiating section and the distal radiatingsection are proportional to an effective wavelength of the radiationtransmitted by the antenna assembly. The distal radiating section mayinclude a metal, a dielectric material or a metamaterial.

The microwave antenna assembly may include a dielectric coating disposedat least partially over the antenna assembly. The junction memberelectrically insulates the distal radiating section and the proximalradiating section.

In another embodiment, the proximal radiating section has a lengthcorresponding to a distance of one-quarter wavelength of the radiationtransmittable through the antenna assembly. The proximal radiatingsection radiates along the length upon transmission of the radiation.

In yet another embodiment, the junction member further includes a firststep and a second step such that the junction member includes at leasttwo different radial thicknesses. The first step receives one of theinner conductor, the outer conductor, the DC power conductor and the DCneutral conductor. The distal radiating section may include a tapereddistal end.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present disclosure are described herein withreference to the drawings wherein:

FIG. 1 is a perspective view of an electrosurgical system according toan embodiment of the present disclosure;

FIG. 2A is a block diagram illustrating the various functionalcomponents of a conventional microwave generation and delivery system;

FIG. 2B is a graphical illustration of the microwave signal power levelat the various functional components of FIG. 2A;

FIG. 3A is a block diagram illustrating the various functionalcomponents of a power-stage ablation system according to one embodimentof the present disclosure;

FIG. 3B is a graphical illustration of the microwave signal power levelat the various functional components of FIG. 3A;

FIG. 4 is an exploded view of the power-stage device of FIG. 1 accordingto an embodiment of the present disclosure;

FIG. 5A is a block diagram illustration the various functionalcomponents of a microwave generation and delivery system according toanother embodiment of the present disclosure;

FIG. 5B is a graphical illustration of the microwave signal power levelat the various functional components of FIG. 5A;

FIG. 6 is a cross-sectional view of the detail area of the antennaportion of the power-stage device of FIG. 1;

FIG. 7 is an exploded view of the antenna portion of the power-stagedevice of FIG. 1;

FIG. 8A is a cross section of a typical planar n-type FET;

FIG. 8B is an illustration of a cylindrical FET according to oneembodiment of the present disclosure; and

FIG. 8C is an illustration of a cylindrical FET according to yet anotherembodiment of the present disclosure.

DETAILED DESCRIPTION

Embodiments of the presently disclosed microwave antenna assembly aredescribed in detail with reference to the drawing figures wherein likereference numerals identify similar or identical elements. As usedherein and as is traditional, the term “distal” refers to the portionthat is furthest from the user and the term “proximal” refers to theportion that is closest to the user. In addition, terms such as “above”,“below”, “forward”, “rearward”, etc. refer to the orientation of thefigures or the direction of components and are simply used forconvenience of description.

During treatment of diseased areas of tissue in a patient, the insertionand placement of an electrosurgical energy delivery apparatus, such as amicrowave antenna assembly, relative to the diseased area of tissue iscritical for successful treatment. Generally, the microwave antennaassemblies described herein allow for direct insertion into tissue andinclude a half-wave dipole antenna at the distal end. An assembly thatfunctions similarly to the may be found in U.S. Pat. No. 6,878,147 toPrakash, issued on Apr. 12, 2005, which is herein incorporated byreference.

While the present disclosure describes specific modifications andchanges to that which is described in Prakash, this disclosure shouldnot be construed as being limited to incorporation with the Prakashmicrowave energy delivery devices. In addition, while the presentdisclosure is described in the context of microwave energy generationand delivery, the present disclosure may incorporate any suitableelectrosurgical frequency. Other suitable applications are contemplated,such as telecommunications, sensing, imaging, sterilizing and cleaning.

Power-Stage Ablation System

Referring now to FIG. 1, a power-stage antenna integrated microwaveablation system (hereinafter “power-stage ablation system”), accordingto an embodiment of the present disclosure, is shown as system 10.Power-stage ablation system 10 includes a power-stage microwave signalgenerator 100 (hereinafter “power-stage generator”) connected to apower-stage microwave energy delivery device 110 (hereinafter“power-stage device”) via a transmission line 120 and, in someembodiments, a cooling fluid supply 131. Power-stage generator 100includes a housing 130 that houses a power generation circuit 150 thatincludes a microwave signal circuit 150 a and a DC power circuit 150 b.A delivery device port 160 defined in generator 100 operably connects toa device connector 170 at one end of the transmission line 120.

Power-stage device 110 includes a handle 112 and an elongate shaft 114including an antenna 116 on a distal end thereof. Distal portion ofantenna 116 may form a sharpened tip 118 for percutaneous insertion intopatient tissue 180. If present, a cooling fluid supply 131 may supplycooling fluid to power-stage device 110 via supply and return tubes 132,134, respectively, connected to the proximal end of handle 112.

Power-stage device 110 may be intended for use with either thepower-stage ablation system 10 of the present disclosure and/or in aconventional system that supplies high power microwave energy to aconventional microwave energy delivery device (e.g., a power-stagedevice may emulate a conventional microwave energy delivery devicethereby allowing the power-state device to be utilized in either aconventional system or a power-stage ablation system).

While the present disclosure describes a power-stage ablation system 10and methods of use with a percutaneous type delivery device, the systemsand methods disclosed herewithin may be used with, or incorporated into,any suitable type of electrosurgical energy delivery device capable ofdelivering electrosurgical energy, such as, for example, an open device,a catheter-type device, an endoscopic device, a surface delivery deviceand an RF energy delivery device.

Conventional Microwave Ablation System

FIG. 2A is a block diagram illustrating the various functionalcomponents of a conventional microwave energy generation and deliverysystem 20. Conventional system 20 includes a microwave generator 200, atransmission line 220 and a microwave energy delivery device 210.Microwave generator 200 includes a power generation circuit 202 thatgenerates and provides DC power from the DC power supply 204 and amicrowave signal from the signal generator 206. DC power and themicrowave signal are supplied to a first amplifier 208 that amplifiesthe microwave signal to a desirable power level.

First amplifier 208 may include one or more power amplifiers or othersuitable means to amplify the microwave signal generated by the singlegenerator 206 to a desirable energy level.

The microwave signal from the first amplifier 208 is supplied to a firstend of the transmission line 220 connected to the generator connector209. The second end of the transmission line 220 connects to thedelivery device connector 212 of the microwave energy delivery device210. The microwave signal is passed through the device transmission line214 to the antenna 216 at the distal end of the microwave energydelivery device 210.

FIG. 2B is a graphical illustration of the microwave signal power levelat the various functional components of the conventional microwaveenergy generation and delivery system 20 of FIG. 2A. The desirableamount of energy delivered to antenna 216 is illustrated on the graph as100% Power Level and shown as E_(TARGET). FIG. 2B further illustratesthe signal strength of the microwave signal at each component of theconventional system 20 of FIG. 2A.

With continued reference to FIGS. 2A and 2B, microwave signal strengthat the signal generator 206 is represented as E_(SG) in the first blockof the illustration. The microwave signal is amplified by the firstamplifier 208, based on a desirable amplifier gain, to a suitablemicrowave signal strength E_(FA) as illustrated in the second block. Ina conventional system 20, signal amplification is only performed in themicrowave generator 200, therefore, the first amplifier 208 must amplifythe microwave signal to a suitable microwave power strength to overcomepower losses between the first amplifier 208 and the antenna 216 (i.e.,E_(FA) is greater than E_(TARGET) to compensate for system lossesbetween the first amplifier 208 and the antenna 216).

Components between the first amplifier 208 and the antenna 216 in aconventional system 20 of FIG. 2A may result in a loss of at least aportion of the microwave signal strength. For example, in FIGS. 2A and2B signal loss may occur at any one of the generator connector 209, thetransmission line 220, the deliver device connector/handle 212 and thedevice transmission line 214. Types of energy losses may be due toenergy reflecting back toward the signal generator 206, the generationof thermal energy in a component or the unintentional transmission ofmicrowave energy (i.e., a component acting as an antenna and dischargingmicrowave energy).

More specifically, the microwave signal strength E_(FA) at the firstamplifier 208 is decreased to E_(GC) at the generator connector 209,E_(TL) at the transmission line 220, E_(DD) at the delivery deviceconnector/handle 212 and E_(TARGET) at the antenna 216. In an actualsystem the signal loss will depend on the number of components and typeof components between the first amplifier 208 and the antenna 216. (Thesystem components provided in FIGS. 2A and 2B are provided as an exampleand do not include all components between the amplifier and the antennain an actual system.)

In a conventional microwave ablation system losses, as illustrated inFIG. 2B, are from a high power microwave signal E_(FA). As such, theenergy losses at each component are a percentage of the high powermicrowave signal E_(FA). In a conventional system that transmits a highpower microwave signal losses can be significant and can potentially bedangerous to the patient and/or the clinician. For example, losses inthe transmission line 220 may be due to internal heating, transmissionof the microwave signal and/or energy reflected by a connector thereofor the microwave energy delivery device or heating may occur fromunintentional energy transmission (i.e., at least a portion of thetransmission line acting as an antenna and transmitting energy at thefundamental frequency or a harmonic frequency thereof). Transmissionline heating and inadvertent transmission of energy may result inpatient or clinician burn and/or energy transmissions that exceed one ormore limitations provided in a FCC regulations and/or a standard forelectromagnetic compatibility (EMC).

Energy losses in the conventional system 20 are exacerbated becauseconventional systems 20 operate with a high power microwave signal. Forexample, a semi-rigid coaxial cable, which is typically very efficientat transferring low power microwave signals, is less efficient whentransmitting a high power microwave signal. In addition, when operatingat high power levels the transmission line may act as an antenna andradiate microwave energy thereby potentially causing harm to thepatient, the clinician or in violation of FCC regulations.

In use, signal generator 206 generates a low power signal, E_(SG), whichis supplied to the first amplifier 208. The power delivered to theantenna 216 is equal to 100% on the power level scale and labeled“Target Power Delivery” and shown as E_(TARGET) in FIG. 2B. In order tocompensate for energy losses in the system 20 the first amplifier 208must amplify the microwave signal to a power level of E_(FA), whereinE_(FA) is much greater than the target power delivery, E_(TARGET) (i.e.,E_(FA) approximately 140% of E_(TARGET)). Losses in the system 20 mayinclude a loss at the generator connector 209, a loss at thetransmission line 220, a loss at the delivery device connector andhandle 212 and a loss at the device transmission line 214.

As a result thereof, a majority of the energy provided to the antenna216 is transmitted into tissue and generates heat through dipolarrotation. A portion of the energy delivered to tissue may inducelocalized currents and finally at least a portion of the energy mayresult in heating of the antenna portion (heating of the actual antenna,while not ideal, is tolerable since the heat will conduct to thesurrounding tissue).

The power-stage ablation system of the present disclosure distributes atleast a portion of the power amplification from the microwave generatorto another part of the system thereby reducing the energy in themicrowave signal transmitted by the transmission line. As such, energylosses of the power-stage ablation system are much lower in magnitudethan the energy losses of a conventional microwave ablation system.

Power-Stage Ablation System

FIG. 3A is a block diagram illustrating the various functionalcomponents of one embodiment of the power-stage ablation system of FIG.1 and is shown as power-stage ablation system 30. Power-stage ablationsystem 30 includes a power-stage generator 300, a transmission line 320and a power-stage device 310. Power-stage generator 300 includes atleast a power generation circuit 302 that generates DC power from the DCpower supply 304 and a microwave signal from the signal generator 306and a processor 307. DC power and the microwave signal are supplied tothe power-stage generator connectors 309. Signal generator 306 mayinclude one or more amplifiers to amplify the signal to a desirablepower level. The various other components of a conventional microwavegenerator known in the art are not discussed in the present disclosure.

Transmission line 320 transfers a DC power signal and a microwave signalfrom power-stage generator connectors 309 to the handle 312 of thepower-stage device 310. Power-stage device 310 includes a deliverydevice handle 312, a device transmission line 314 and an antenna 316,wherein the delivery device handle 312 includes a handle power amplifier312 a. The handle power amplifier 312 a receives a DC power signal and amicrowave energy signal from the power generation circuit 302 andamplifies the microwave signal to a desirable or target energy level.Various embodiments of the handle power amplifier 312 a are described indetail hereinbelow.

FIG. 3B is a graphical illustration of the microwave signal strength atthe various functional components of the power stage ablation system 30of FIG. 3A. The desirable amount of energy delivered to antenna 316 isillustrated on the graph as 100% Power Level and shown as E_(TARGET).FIG. 3B further illustrates the signal strength at a component in thepower-stage ablation system 30 and the difference between two adjacentbars is equal to the energy losses that occur at each component. Thecomponents included in FIGS. 3A and 3B are for illustrative purposes anddo not reflect all of the actual components in the system 30.

With continued reference to FIGS. 3A and 3B, signal generator 306generates a microwave energy signal with an energy level of E_(SG). Themicrowave signal is supplied to the generator connector 309, along withthe DC power signal from the DC power supply 304, and transmitted to thepower-stage device 310 through the transmission line 320.

Unlike the conventional microwave ablation system, as describedhereinabove and illustrated in FIGS. 2A and 2B, the power-stage ablationsystem 30 distributes the task of amplifying the microwave signalbetween various components in the power-stage ablation system 30.Distribution of the power amplification function decreases the energy ofthe signal transmitted by the transmission line 320 and in othercomponents in the system.

In the power-stage amplification system 30, the energy of the microwavesignal provided to the generator connector 309, the transmission line320 and the delivery device handle, E_(GC), E_(TL) and E_(DD),respectively, are less than the energy at the respective components inthe conventional system of FIG. 2A.

The transmission line 320 and delivery device handle 312 pass themicrowave signal, with microwave signal strength equal to E_(DD) and theDC power signal to the handle power amplifier 312 a. As illustrated inFIG. 3B, the energy level at the handle power amplifier 312 a, E_(DD),is significantly less than E_(TARGET). The handle power amplifier 312 aamplifies the signal to an energy level greater equal to E_(HPA).E_(HPA) is slightly greater than E_(TARGET), with the difference betweenE_(HPA) and E_(TARGET) about equal to the energy losses that occur inthe device transmission line 314.

In the present embodiment, amplification of the microwave signal isproportioned between the signal generator 306 in the power-stagegenerator 300 and the handle power amplifier 312 a in the handle 312 ofthe power-stage device 310. The amplification ratio between the signalgenerator 306 and the handle power amplifier 312 a may range between1:10 wherein a majority of the microwave signal amplification isperformed in the handle and 100:0 wherein all amplification is performedin the signal generator (thereby emulating a conventional system).

The present embodiment and the various other embodiments describedhereinbelow are examples of systems that distribute the signalamplification function. Signal amplification may be distributed betweentwo or more locations, such as, for example, between at least two of thesignal generator, the power-stage device handle and the power-stagedevice antenna. The specific embodiments should not be considered to belimiting as various other combinations and locations may be used todistribute the signal amplification function and are therefore withinthe spirit of the present disclosure.

Distributed signal amplification may be performed by one or more poweramplifiers e.g. an FET power amplifier. “FET” is used generically toinclude any suitable power amplification device or circuit configured toamplify a microwave signal. Examples of FETs include a MOSFET(Metal-Oxide-Semiconductor Field-Effect Transistor), a JFET (JunctionField-Effect Transistor), a MESFET (Metal-Semiconductor Field-EffectTransistor), a MODFET (Modulation-Doped Field Effect Transistor), a IGBT(insulated-gate bipolar transistor), a HEMT (high electron mobilitytransistor formed of AlGaN/GaN) and a GaN HFET (gallium nitridehetero-junction field effect transistors). Various FET's will beillustrated hereinbelow. Signal generator 306, handle power amplifier312 a or other distributed signal amplification may each include one ormore suitable FET devices or any combination or equivalent thereof.

FIG. 4 is a cross-sectional view of the handle 412 of the power-stagedevice 110, 310 of FIGS. 1 and 3A, respectively, according to anembodiment of the present disclosure. Handle 412 receives DC power and amicrowave signal from the transmission line 420 through connectors 415a, 415 b housed in the proximal portion 412 b of handle 412. DC powertransmission line 420 a provides DC power through the DC connector 415 ato the DC positive 421 a and DC negative 421 b terminals of the handlepower amplifier 430. Microwave power transmission line 420 b provides amicrowave signal to the microwave connector 415 b and handletransmission line 420 c connects the microwave power transmission line420 b to the handle power amplifier 430.

Handle power amplifier 430 is mounted in the handle 412 and may besupported by one or more amplifier supports 432. Amplifier supports 432may be formed as part of the handle 412 or may be separate components.Amplifier supports 432 may include active or passive cooling to cool thehandle power amplifier 430. In one embodiment, the handle 412 includesactive cooling, e.g. the amplifier supports 432 receive cooling fluidfrom a cooling fluid supply, as illustrated in FIG. 1, and actively coolthe handle power amplifier 430. In another embodiment, the handle 412includes passive cooling, e.g. the amplifier supports 432 are configuredto conduct thermal energy away from the handle power amplifier 430.Amplifier supports 432 may be incorporated into handle 412, therebyallowing heat to dissipate through the handle 412 body.

Handle power amplifier 430 amplifies the microwave signal to a desirableenergy level, (e.g., to a suitably high power microwave signal level forperforming tissue ablation or a desired surgical procedure), andsupplies the high power microwave signal to the device transmission line414 and to the antenna 116 connected to the distal end of the devicetransmission line 114, as illustrated in FIG. 1.

In some ablation procedures, heating of the device transmission line 414may be desirable. For example, it may be desirable to ablate at least aportion of the insertion track created in the patient tissue by thesharpened tip when the power-stage device is percutaneously insertedinto the patient tissue. In one embodiment, the device transmission line414 is configured as a heat sink for the handle power amplifier 430 andmay dissipate at least some thermal energy generated by the handle poweramplifier 430 to tissue.

With reference to FIG. 3A, power stage generator 300 may be configuredto control the microwave signal amplification distribution between thesignal generator and additional amplifier in the power-stageamplification system 30. Processor 307 of the power-stage generator 300may control the amplification of one or more of the amplifiers in thepower-stage amplification system 30. For example, amplification of themicrowave signal by the signal generator 306 may be fixed to provide amicrowave signal to the transmission line at a fixed energy level. Themicrowave signal may be variably amplified to a target energy level by asecond amplifier as also described herein. In another embodiment, thegain of the signal generator and the gain of the second amplifier, asdescribed herein, are selectively controlled such that the combined gainof the amplifiers amplifies the microwave signal to a target energylevel. The ratio of the gain between the two amplifiers may range from100% of the gain at the signal generator (wherein the power-stageamplification system emulates a conventional system) and 10% gain at thesignal generator and 90% of the gain at the second amplifier, asdescribed herein.

The gain of the second amplifier, as described herein, may be controlledby varying the voltage of the DC power signal. Control may be open-loopwherein the processor 307 of the power-stage generator 300 estimates thevoltage of the DC power signal required to generate the gain requiredfrom the second amplifier to amplify the microwave signal to the targetenergy level. In another embodiment, the power-stage amplificationsystem may include closed-loop control wherein the output of the secondamplifier or a measurement of the microwave signal provided to antennais provided to the processor 307 as feedback to the closed-loop controlsystem. The measurement of the microwave signal may be any suitablemicrowave signal measurement such as, for example, forward and/orreflected power from a dual directional coupler.

Amplifier gain may be selectively controlled by the processor or theclinician. The second amplifier, as described herein, may not providesignal amplification if selected output to the antenna is below anoutput threshold. For example, at a low power output the signalgenerator 306 may provide about 100% of the required amplification(i.e., operating similar to a conventional system). As the power outputis selectively increased, the microwave signal amplification may bedistributed between the signal generator 306 and the second amplifier inthe power-stage device. The power output may be selectively increased bya manual input to the power-stage generator 300 by a clinician or may beselectively increased and/or actively changed by an output algorithmperformed by the processor 307.

FIG. 5A is a block diagram illustrating the various functionalcomponents of another embodiment of the power-stage ablation system ofFIG. 1 and is shown as 50. Power-stage ablation system 50 includes apower-stage generator 500, a transmission line 520 and a power-stagedevice 510. Power-stage generator 500 includes a power generationcircuit 502 that generates DC power from the DC power supply 504 and amicrowave signal from the signal generator 506 and a processor 507. DCpower and the microwave signal are supplied to the power-stage generatorconnectors 509. Signal generator 506 may include one or more amplifiersto amplify the microwave signal to a desirable power level.

Transmission line 520 transfers a DC power signal and a microwave signalfrom power-stage generator connectors 509 to the handle 512 of thepower-stage device 510. Power-stage device 510 includes a deliverydevice handle 512, a device transmission line 514 and an power-stageantenna 516, wherein the power-stage antenna 516 includes an antennapower amplifier 530 configured to amplify the microwave signal generatedby the signal generator 506 to a desirable power level. The antennapower amplifier 530 receives a DC power signal and a microwave energysignal from the power-stage generator circuit 502 and amplifies themicrowave signal to a desirable or target energy level. Variousembodiments of the antenna power amplifier 530 are described in detailhereinbelow.

FIG. 5B is a graphical illustration of the microwave signal power levelat the various functional components of FIG. 5A. The targeted energydelivered to antenna 516 is illustrated on the graph as 100% power leveland shown as E_(TARGET). Each bar illustrates the energy level at acomponent in the power-stage ablation system 50 and the differencebetween two adjacent bars is equal to the energy loss at eachcomponents. The components included in FIGS. 5A and 5B are forillustrative purposes and do not reflect all components that may beincluded in a functional power-stage ablation system 10 as illustratedin FIG. 1.

With continued reference to FIGS. 5A and 5B, signal generator 506generates a microwave signal with an energy level of E_(SG). Themicrowave signal is supplied to the generator connector 509, along withthe DC power signal from the DC power supply 504, and the microwavesignal and the DC power signal are transmitted to the power-stage device510 through the transmission line 520.

Losses between the signal generator 506 and the generator connectors 509reduce the microwave signal power level from E_(SG) to E_(GC) asillustrated in FIG. 5B. Losses in the transmission line further reducethe microwave signal power level to E_(TL) and losses in the deliverydevice handle and device transmission line further reduce the microwavesignal power level to E_(DD) and E_(DTL), respectively. The microwavesignal delivered to the antenna 516 by the device transmission line 514is amplified by antenna power amplifier 516 to a desirable or targetmicrowave signal power level of E_(TARGET).

A significant difference between the transmission of the microwavesignal in a conventional system and the transmission of the microwavesignal in the present embodiment of the power-stage ablation system 50is the energy level of the microwave signal in the transmission path. Inthe conventional system 20 the energy level of the microwave signal inthe transmission path is greater than the target power level tocompensate for losses in the transmission path, as illustrated in FIGS.2A and 2B. In the power-stage ablation system 50 the energy level of themicrowave signal in the transmission path is a fraction of the targetpower level as illustrated in FIGS. 5A and 5B. As such, the energylosses in the transmission path of the power-stage ablation system 50are much less than the energy losses in the transmission path of theconventional system. The reduction in the microwave signal energy levelin the transmission path also decreases the likelihood of unintentionalmicrowave energy discharged therefrom.

In the present embodiment, amplification of the microwave signal isdistributed between the signal generator 506 in the power-stagegenerator 500 and by the antenna power amplifier 530 in the antenna 516of the power-stage device 510. Signal generator 506 generates amicrowave signal with an energy level of E_(GS). The microwave signalpower level from the signal generator 506, E_(SG), has sufficient energyto overcome losses in the transmission path between the signal generator506 and the antenna power amplifier 530. Antenna power amplifier 530receives the microwave signal with a microwave signal power level ofE_(DTL) and amplifies the microwave signal to a microwave signal powerlevel of E_(TARGET). Antenna power amplifier 530 may require and/orinclude one or more amplification stages and may include one or moreFETs.

The transmission line 520 is configured to pass a low power microwavesignal and a DC power signal. Transmission line 520 may be configured asa multi-conductor cable that provides both the microwave signal and DCpower to the power-stage device 512. For example, a first conductor maybe configured as a standard coaxial cable and a second conductor may beconfigured as a suitable DC power transmission conductor. The DC powertransmission conductor may “piggy-back” the coaxial cable as is known inthe art. Alternatively, device transmission line 514 may include two ormore transmission lines to transmit a low power microwave signal and aDC power signal.

As illustrated in FIG. 6, device transmission line 614 is configured totransmit the low power microwave signal and the DC power signal to theantenna power amplifier 630. Device transmission line 614 includes acoaxial arrangement with an inner conductor 614 a and an outer conductor614 b separated by a suitable dielectric 614 c. A DC power signal may betransmitted through a DC power layer 621 positioned radially outwardfrom the outer conductor 614 b. For example, DC power layer may includeat least one DC positive trace 621 a and at least one DC negative trace621 b insulated from, and printed on, the radial outer surface of theouter conductor 614 b. In another embodiment, the DC power signal istransmitted through a suitable conductor pair positioned radiallyoutward from the outer conductor 614 b.

The antenna power amplifier may be positioned adjacent the antenna. Inone embodiment, the antenna power amplifier is positioned between thedistal end of the device transmission line and the proximal end of theantenna. In another embodiment, the antenna power amplifier may bepositioned between the distal and proximal radiating sections of theantenna. Antenna power amplifier may include a cylindrical FET describedhereinbelow capable of providing sufficient signal amplification of amicrowave signal for use in microwave ablation.

FIG. 6 is a cross-sectional view of the antenna 516 of the power-stagedevice 510 of FIG. 5A and the antenna 116 of FIG. 1 according to oneembodiment of the present disclosure. Antenna 616 includes a proximalradiating section 616 a, a distal radiating section 616 b and an antennapower amplifier 630 positioned therebetween. A sharpened tip 618, distalthe distal radiating section 616 b, is configured to facilitatepercutaneous insertion into tissue. The antenna power amplifier 630 maybe a junction member that joins the proximal radiating section 616 a andthe distal radiating section 616 b. The device transmission line 614connects to at least a portion of the antenna 616 and provides DC powerand a microwave signal to the antenna power amplifier 630.

The antenna power amplifier 630 connects the distal radiating section616 b and the sharpened tip 618 to the proximal portion of the antennaand/or the transmission line 614 and may provide support and rigidity tothe antenna 616. Antenna power amplifier 630 may connect with amechanically-engaging joint such as, for example, a press-fit joint, aninterface-fit joint, a threaded interface, a pinned joint and an overlapjoint. Antenna power amplifier 630 may be adapted to be in apre-stressed condition to further provide mechanical strength to theantenna.

Antenna power amplifier 630 receives DC power from the DC positive 621 aand the DC negative 621 b of the device transmission line 614, andmicrowave power from the inner and outer conductors 614 a, 614 b,respectively. In this embodiment, the inner portion of the devicetransmission line 614 is configured as a coaxial waveguide surrounded bytwo or more conductors 621 that provide the DC power. The two or moreconductors 621 may be configured as a twisted pair, a plurality oftwisted pair combinations, or any other suitable combination.

DC power may be provided between a plurality of conductors or conductorpairs to distribute the current required by the antenna power amplifier630. For example, the coaxial waveguide of the device transmission line614 may be at least partially surrounded by four two-wire twisted pairconductors each supplying about one fourth of the DC power to theantenna power amplifier 630. The arrangement of the conductors aroundthe coaxial waveguide may be configured to minimize noise or to preventinduction of a microwave signal on the conductors.

In a conventional microwave energy delivery system, as discussedhereinabove, the device transmission line transmits a high powermicrowave signal and any heat generated therein is from the high powermicrowave signal In the present embodiment, the device transmission line614 transmits a low power microwave signal and a DC Power signal to theantenna power amplifier 630 where the microwave signal is amplified to adesirable power level. Some thermal energy may still be generated in thedevice transmission line 614 from both the low power microwave signaland/or the DC power signal. A fluid cooling system, as illustrated inFIG. 1, may be configured to provide cooling fluid to any portion of thedevice transmission line 614.

In another embodiment, a DC power signal may generate a majority of thethermal energy in the device transmission line 614. As such, the coolingsystem may be configured to provide cooling to the conductors providingthe DC power signal.

Device transmission line 614 may include a fluid cooling system toabsorb thermal energy. With reference to FIG. 1, cooling fluid from thecooling fluid supply 131 may circulate through at least a portion of thedevice transmission line 114. Cooling fluid may absorb thermal energyfrom the device transmission line (e.g., the conductors that provide theDC power, the coaxial waveguide or both). Cooling fluid may be used toseparate the microwave energy waveguide (i.e., the coaxial) and theconductors providing the DC power thereby providing an electromagneticshield between at least a portion of the coaxial waveguide transmittingmicrowave energy and the conductors providing DC Power.

As illustrated in FIG. 6, proximal and distal radiating sections 616 a,616 b connect to antenna power amplifier 630. Antenna power amplifier630 receives a microwave signal at a first power level from the innerand outer conductor and a DC power signal from the DC power and DCneutral and amplifies the microwave signal to a second power level. Themicrowave signal at the second power level is supplied to the radiatingsections 616 a, 616 b. Antenna power amplifier 630 may generate thermalenergy during signal amplification. Thermal energy may be absorbed by,or provided to, the surrounding tissue and may contribute to the desiredclinical effect.

FIG. 7 is an exploded view of the antenna 116 portion of the power-stagedevice 110 of FIG. 1. The device transmission line 714 connects to theproximal portion of the proximal radiating section 716 a and supplies aDC power signal and a microwave signal to the antenna portion 716. Themicrowave signal is provided through a coaxial waveguide that includesan inner conductor 714 a and an outer conductor 714 b separated by adielectric 714 c. The DC power signal is provided through at least apair of DC conductors 721 a, 721 b that includes a DC positive 721 a anda DC negative 721 b. DC conductors 721 a and 721 b may be formed on theinner surface of the insulating coating 754.

The antenna 716 includes a proximal radiating section 716 a and a distalradiating section 716 b separated by an antenna power amplifier 730.Antenna power amplifier 730 receives the microwave signal and DC powerfrom the device transmission line 714, amplifies the microwave signal toa desirable energy level and provides the amplified microwave signal tothe proximal radiating section 716 a and the distal radiating section716 b of the antenna 716. A sharpened tip 718 connects to the distalportion of the distal radiating section 716 b and is configured topenetrate tissue.

The proximal end the antenna power amplifier 730 connects to the innerconductor 714 a, the outer conductor 714 b, the DC positive 721 a, theDC negative 721 b, and the proximal radiating section 716 a. The centerportion of the antenna power amplifier 730 receives the distal end ofthe inner conductor 714 a and the outer conductor 714 b is receivedradially outward from the center of the antenna power amplifier 730. Theantenna power amplifier 730 receives the microwave signal between theinner and outer conductor of the coaxial waveguide. Radially outwardfrom the surface of the antenna power amplifier 730 that receives theouter conductor 714 b, the surface of the antenna power amplifier 730connects to the DC conductors 721 a and 721 b and receives the DC powersignal therefrom. The proximal radiating section 716 a of the antenna716 at least partially surrounds the antenna power amplifier 730 andreceives the amplified microwave signal therefrom. Proximal radiatingsection 716 a may also conduct thermal energy away from the antennapower amplifier 730.

The distal end of the antenna power amplifier 730 connects to theproximal end of the distal radiating section 716 b and receives theamplified microwave signal therefrom. Distal radiating section 716 b mayalso conduct thermal energy away from the antenna power amplifier 730.Distal radiating section 716 b and proximal radiating section 716 atogether form the two poles of a dipole microwave antenna. In thisparticular embodiment, antenna 716 is a conventional half-wave dipolemicrowave antenna and includes a proximal radiating section 716 a and adistal radiating section 216 b. The antenna power amplifier describedherein may be used with any suitable microwave antenna, such as anelectrosurgical antenna configured to radiate microwave energy to tissuein an electrosurgical procedure.

Tip connector 722 connects the sharpened tip 718 to the distal end ofthe distal radiating section 716 b. Sharpened tip 718 may be part of thedistal radiating section 716 b or sharpened tip 718 may connect todistal radiating section 716 b and configured to not radiate energy. Forexample, tip connector 722 may electrically connect or electricallyinsulate sharpened tip 718 and distal radiating section 716 b. Inanother embodiment, sharpened tip 718 may include a suitable attachmentmeans thereby eliminating the tip connector 722.

In yet another embodiment, the antenna power amplifier 730 is positionedproximal to the proximal radiating section and the proximal and distalradiating sections are separated by a conventional spacer as known inthe art.

FIG. 8A is a cross section of a typical n-type FET 830 a. The typicalFET used for microwave applications use a planar topology in which anactive epitaxial layer is placed on a semi-insulating substrate. Forexample, semi-insulating substrate may include gallium arsenide (GaAs),silicon, germanium or any other suitable material commonly used insemiconductor devices. FET may also include gallium nitride (GaN). GaNmay be particularly suited when working with higher temperatures, highervoltages and/or higher frequencies, while producing less heat._On thissubstrate a conductive layer is deposited and photo-etched to leavestructures referred to as a source, gate and drain. Gate terminal 864 acontrols the opening and closing of the transistor by permitting orblocking the flow of electrons between the source 860 a and drain 862 a.The gate terminal 862 a creates or eliminates a channel in the activelayer 866 a between the source 860 a and the drain 862 a and the densityof the electron flow is determined by the applied voltage. The body 868a includes the bulk of the semiconductor in which the gate 864 a, source860 a and drain 862 a lie. With reference to FIG. 7, the antenna poweramplifier 730 may be configured to house an n-type FET 830 a illustratedin FIG. 8A.

In yet another embodiment of the present disclosure, the antenna poweramplifier 730 illustrated in FIG. 7 is formed from a cylindrical FET 830b as illustrated in FIGS. 8B and 8C. In FIGS. 8B and 8C each of thecylindrical FETs 830 b, 830 c are configured in a cylindricalarrangement to facilitate placement of the cylindrical FETs 830 b, 830 cin the antenna 116, 716 of the power-stage device 110 antenna 116, 716of FIGS. 1 and 7, respectively. Starting at the radial center of thecylindrical FET 830 b and working radially outward, the layers include asource 860 b, 860 c, an first epitaxial layer 868 b, 868 c the gate 864b, 864 c, a second epitaxial layer 869 b, 869 c, and a drain 862 b, 862c. The source 860 b, 860 c may be formed from a center pin, tube orelongate conductive structure on which a first epitaxial layer 868 b,868 c is deposited. As illustrated in FIG. 8C, the shape of the centerstructure need not be circular. Varying the overall shape and structureof the center structure varies the surface area between the source 860b, 860 c and the first epitaxial layer 868 b, 868 c. On the firstepitaxial layer 868 b, 868 c a metal layer is deposited that serves as agate 864 b, 864 c. The gate 864 b, 864 c may have through holes filledwith a second epitaxial layer 869 b, 869 c in order to provide a current“pinch off” effect similar to that used in a planar FET. Alternatively,the gate 864 b, 864 c may be partitioned into several continuous stripesor strips thereby allowing a control voltage at varying potentials to beapplied and to “pinch off” the flow of electrons and control the poweroutput of the cylindrical FET. Many other configurations are possible toallow gate control of the cylindrical FET and are likely to be dictatedby geometry and/or the choice of materials. In one embodiment, the metalforming gate 864 b, 864 c may be gold. Deposited on the second epitaxiallayer 869 b, 869 c is a second conductive layer that serves as drain 862b, 862 c. In one embodiment, the drain 862 b, 862 c acts as the externalsurface, i.e., a radiating section of the antenna. The drain 864 b, 864c is concentrically deposited outside the gate 862 b, 862 c and secondepitaxial layer 869 b, 869 c sandwich layers.

In use, the DC voltage applied across the source and drain determinesthe gain of the output stage. The microwave frequency signal is appliedto the gate. As such, the gain of the power-stage device is controlledby the signals provided from the power-stage microwave generator.

The cylindrical FET 830 b, 830 c, while configured to operate similarlyto a traditional FET illustrated in FIG. 8A and described hereinabove,is particularly suited for use in microwave ablation devices describedherein and used in the art.

In yet another embodiment, the cylindrical FET 830 b, 830 c mayincorporate the use of metamaterial in the FET's construction, theconstruction of the antenna power amplifier and/or the construction ofthe distal or proximal radiating section. A metamaterial is anengineered material with a particular structure that provides control ofthe permittivity and permeability of the material. With metamaterials,the structure, rather than the composition, determines the property ofthe material The cylindrical FET may include at least one layer formedof a metamaterial. For example, the drain 862 b, 862 c may be coatedwith a metamaterial surface (not shown) or may be formed from ametamaterial such that the metamaterial serves as a electromagnetic wavesteerer or refractor, modulator, filter, magnifier or coupler. In oneembodiment, the metamaterial produces a non-uniform electromagneticfield around the antenna.

While several embodiments of the disclosure have been shown in thedrawings and/or discussed herein, it is not intended that the disclosurebe limited thereto, as it is intended that the disclosure be as broad inscope as the art will allow and that the specification be read likewise.Therefore, the above description should not be construed as limiting,but merely as exemplifications of particular embodiments. Those skilledin the art will envision other modifications within the scope and spiritof the claims appended hereto.

1. A microwave antenna assembly for applying microwave energy therapycomprising: a proximal radiating section having an inner conductor, anouter conductor, a DC power conductor and a DC neutral conductor, eachextending therethrough, the inner conductor disposed within the outerconductor and the DC power conductor and DC neutral conductor disposedradially outward from the outer conductor; a distal radiating sectiondistal the proximal radiating section; and a junction member configuredto mate the distal radiating section and proximal radiating section suchthat the proximal radiating section and the distal radiating sectionsare fixedly positioned relative to one another by amechanically-engaging joint, the junction member further configured toinclude: a microwave signal amplifier configured to receive a microwavesignal at a first energy level from the inner conductor and the outerconductor and configured to receive a DC power signal from the DC powerconductor and the DC neutral conductor, the microwave signal amplifierfurther configured to amplify the microwave signal from the first energylevel to at least one second energy level, the at least one secondenergy level being greater than the first energy level, wherein thejunction member is further configured to provide the microwave signal atthe second energy level to the proximal radiating section and the distalradiating section.
 2. The microwave antenna assembly of claim 1 whereinthe proximal radiating section and distal radiating section are adaptedto radiate upon transmission of radiation through the antenna assembly.3. The microwave antenna assembly of claim 2 wherein the proximalradiating section and the distal radiating section have a length whichis proportional to an effective wavelength of the radiation transmittedby the antenna assembly.
 4. The microwave antenna assembly of claim 1wherein the distal radiating section comprises at least one of a metal,a dielectric material and a metamaterial.
 5. The microwave antennaassembly of claim 1 further comprising a dielectric coating disposed atleast partially over the antenna assembly.
 6. The microwave antennaassembly of claim 1, wherein the junction member electrically insulatesthe distal radiating section and the proximal radiating section,
 7. Themicrowave antenna assembly of claim 1 wherein the proximal radiatingsection has a length corresponding to a distance of one-quarterwavelength of radiation transmittable through the antenna assembly. 8.The microwave antenna assembly of claim 7 wherein the proximal radiatingsection is adapted to radiate along the length upon transmission of theradiation.
 9. The microwave antenna assembly of claim 1 wherein thejunction member further includes a first step and a second step suchthat the junction member comprises at least two different radialthicknesses, wherein the first step is configured to receive at leastone of the inner conductor, the outer conductor, the DC power conductorand the DC neutral conductor.
 10. The microwave antenna assembly ofclaim 1 wherein the distal radiating section has a tapered distal end.